1. Field of the Invention
This invention generally relates to signal communications and, more particularly, to a system and method that uses time domain reflectometry measurements to calibrate for skew errors in a multichannel Optical Transport Network (OTN) transmitter.
2. Description of the Related Art
100 gigabit per second (Gbps) OTN protocols are being developed where the OTN streams are carried in a “parallel fashion” at a bit-rate greater than 100 Gbps. Until recently, optical signals have been carried using modulations techniques carrying 1 bit per symbol. However, the need for faster signal speeds means that return to zero (RZ), non-return to zero (NRZ), and phase-shift keying (PSK) modulation techniques (1 bit per symbol) are no longer suitable.
FIG. 1 is a schematic diagram depicting a system for the transmission of high speed signals (40/100 Gbps and above) using multiplexed orthogonal optical polarization, with 2 bits per symbol per polarization, for a total of 4 bits/symbol. Any skew (differential time delay) experienced in the modulation of the transmitted signal is translated to the receiver, making the recovery of a serial stream from parallel streams difficult.
It would be advantageous if a technique could be developed to minimize differential time delay or skew in the parallel pathways of a multiplexed orthogonally polarized OTN signal.